Monitoring method for the chloride ion penetration in mortar by a thin-film sensor reacting to chloride ion

• A sensor reacting to chloride ion was developed using screen printing.
• The sensor with a weight ratio for Ag:Fe of 1:2 was proven to react to corrosion.
• Electrical resistance was confirmed to change with corrosion caused by salinity.
• The sensor could monitor the depth of salinity penetration from the mortar surface.

The depth of chloride ion permeation from a concrete surface can be monitored in reinforced concrete structures. The purpose of this study is to develop and apply a thin-film sensor based on the measurement of changes in electrical resistance of the sensing elements in order to follow the chloride ion penetration in mortar. The proposed thin-film sensors were placed in mortar specimens intrinsically containing chlorides, and mortar specimens impregnated with chloride solutions then subjected to accelerated corrosion in a NaCl solution. For making a film sensor, a screen printer machine was used. Silver (Ag) paste and iron (Fe) powder were coated on the thin-film sensor that reacts to chloride ion in mortar. As a result of experimental testing, the appropriate ratio of Ag to Fe was >1:2. The electrical resistance of the sensors increased with the degree of corrosion behavior of thin-film sensor. The time to the first change in electrical resistance decreased along with the degree of corrosion as the distance from the mortar surface decreased. The proposed thin-film sensors are thus confirmed to be capable of monitoring the depth of chloride permeation in mortar with sufficient accuracy.